There are many kinds of bearings for rotation devices. An airfoil bearing generates small friction force by making an air film between the rotating shaft and housing. Thus, the airfoil bearing is used for high speed rotation device but it has the dis-advantage of being difficult to control. However, a magnetic bearing can adjust the magnetic force of the electromagnet. Thus it has the advantage of being easy to control. However, it is also difficult to control at high speeds. In particular, if the rotating shaft is tilted to one side during high speeds and contacts the magnetic pole, then the system may be damaged. Thus, a hybrid bearing having an airfoil bearing and magnetic bearing used together has been developed for taking all the advantages of the airfoil bearing and the magnetic bearing.
Referring to FIG. 1, a prior art airfoil-magnetic hybrid bearing for a high speed rotation device will be described in detail.
FIG. 1 is a side sectional view illustrating an exemplary prior art airfoil-magnetic bearing. As illustrated, the prior art airfoil-magnetic hybrid bearing includes an airfoil bearing (30) around the rotating shaft (20) disposed at the center portion of a cylindrical housing (10) and a magnetic bearing (40) disposed around the airfoil bearing (30).
The housing (10) has cores (41) formed parallel to the rotating shaft (20) and coils (42) wound around the cores (41) respectively. The housing extends more deeply than the magnetic bearing (40) and the airfoil bearing (30) is mounted on the extended portion of the housing.
However, the core (41) of the prior art airfoil-magnetic hybrid bearing must be disposed parallel to the longitudinal direction of the housing (10), while the coil (42) must be wound around the core (41). Thus, the total length of the rotation rotor becomes longer. The airfoil bearing (30) is not coupled to the magnetic bearing (40) directly. An axial length (L1) of the housing (10) becomes longer since the housing (10) has the airfoil bearing (30) and the magnetic bearing (40) together.
Further, a radial thickness of the housing (10) around the rotating shaft (20) becomes larger since there is a gap between the airfoil bearing (30) and the magnetic bearing (40). Thus, total volume of the hybrid bearing becomes larger.
Further, the magnetic bearing (40) is positioned away from the rotating shaft due to the gap between the airfoil bearing (30) and the magnetic bearing (40). Thus, the magnetic bearing (40) has a low supporting efficiency.